I'm planning to use Arduino for obtaining resonant frequency and bandwidth of the piezo output and correlating it to the viscosity. There is an article that piezo is being used as an viscosity sensor but I'm not sure if Arduino is capable of doing this operation. My goal is to display the viscosity in a LCD. Please tell me if this is feasible or not. thank you.

I could find articles and patents about this, but they all seem to use a special shaped piezo element.

Do you want to use a normal piezo element ?The Arduino could use a digital output with a certain frequency, but that would not be a sine. How would you want to read the resonance frequency ?Take a look at the ping))) library : http://arduino.cc/en/Tutorial/PingThe piezo needs extra hardware to do that.

In the same way you need extra hardware for your piezo sensor. Controlling that extra hardware is what the Arduino is good at.